Picking date recommendations for air and CA storage of Gala
Early picking of Gala apples may compromise fruit size, red colour and flavour potential. Picking too late may compromise fruit firmness and accentuate the development of a greasy skin.
Selection of the correct clone, appropriate pruning and thinning practices will help to ensure that the decisions on harvest date are based solely on the rate of maturation of the fruit on the tree.
Waiting for size and colour can seriously compromise eating quality and storage potential. There is also evidence that late harvesting causes a severe skin disorder in apples held in air storage (see Section 13). [hyperlink]
The results of a 3-year project (2000-02) funded by HDC (TF122) showed clearly the influence of harvest date on storage quality of Gala apples. Fruit harvested over a 2-week period in 2001 (24 September – 8 October) and 2002 (17 September – 1 October) were virtually free of storage disorders when stored in CA conditions (CO2 / O2) of 8/13, <1/2 and <1/1 for the recommended periods (see Section 9) [hyperlink] and subjected to a simulated marketing period.
This indicates that fruit picked at an advanced stage of maturity as indicated by the starch-iodine test (Ctifl score of 6-8.6 in 2001 and 7.3-7.5 in 2002) are acceptable for storage in CA (except 5/1) for the prescribed periods. This accords with the results of early work which suggested that fruit should be picked when the starch coverage is 50-90 (% black) and firmness is in excess of 7 kg.
However, while it is important that fruits remain in a firm condition and free of physiological disorders it is also important that the skins of the fruit should not become greasy. To avoid the development of greasiness after storage it was necessary to harvest at a much earlier stage of maturity i.e. when starch had declined to a Ctifl score of about 3-5.7 in 2001 and 2.6-2.8 in 2002.
The average Ctifl score for minimising greasiness in fruit from the same Kent orchards in 2001 and 2002 was 3.5, which is equivalent to a starch coverage of about 85%. This figure is close to that (starch above 80%) suggested by the Quality Fruit Group (QFG) to achieve the best eating quality after long-term storage (QFG Newsletter No. 3 – 5 September 2002).
The evidence from the Quality Fruit Group that early picking may provide better flavour in stored Gala apples is also backed by the views of Australian research workers (personal communication) who claim that maximum flavour from store is associated with harvesting at the onset of the climacteric rise in respiration that is coincident with a rapid rise ethylene production.
Fruit for storage in 5/1 until early April must be picked before ripening on the tree is too advanced. In 2001 and 2002 only the first pick of fruit was suitable for long-term storage in 5/1.
Based on the data obtained in the two Kent orchards in both years the picking date criteria for successful 5/1 storage were 3-4.4 on the Ctifl starch chart (78-88% black), 90-93 N (9.2-9.5 kg) firmness, 10-10.9 (%) soluble solids and 25-55% of fruits with internal ethylene concentrations above the ripening threshold of 100 ppb.
Benefits of SmartFreshTM application have been achieved on fruit picked at a later stage of maturity. It appears that, for Gala, time of harvest may not be such a critical factor in deriving a benefit from SmartFreshTM application when compared with other cultivars.